This invention relates to a magnet assembly, for example, of the type which may be employed as a latch for use in connection with a ferromagnetic striking plate. More particularly the invention relates to magnetic locks where a high degree of reliability is an important factor, for example, when used in a computer disk package to securely lock and seal computer memory disks, tapes or the like in as near a dust free environment as possible. Also among the desirable objectives in such magnetic latches is that the magnetic latch should develop a maximum locking force with minimum size and with a relatively inexpensive permanent magnet. To this end, latches have been employed which have a permanent magnet in cooperation with a ferromagnetic, cup-like armature which receives the magnet and which cooperates to define a path for the magnetic flux to enhance the locking force which the permanent magnet can develop.
Typically, the permanent magnet is housed within an open ended ferromagnetic cup-like armature with one pole of the magnet in close, intimate and gap-free contact with the base of the armature. The armature sidewall which surrounds the magnet may be spaced from the sidewall of the magnet or in some instances may be in contact with the side of the magnet. The exposed pole of the magnet is as flat as possible under ideal conditions and the edge of the armature sidewall lies in the same plane as the face of the magnet so that the magnet and armature edge can bear against a ferromagnetic latching plate in as near flush intimate and planar contact as possible, ideally with no gaps. Even a small gap, for example, of the order of 0.001 inch, between the face of the magnet and the latch has an extremely adverse effect on the efficiency of the magnet and can reduce the effective force between the magnet and latching plate by as much as, perhaps, 25 percent. In addition it is equally important that the opposite pole of the magnet, which bears against the bottom of the armature also is in as near as complete flush abutment to avoid gaps which would also have an adverse effect on the efficiency of the magnet. Thus, the construction and manner in which the magnet is assembled is extremely critical. Prior magnet assemblies and assembly techniques have resulted in less than satisfactory results because of the inability to maintain these strict requirements. For example, typical prior assembly techniques include a final grinding of the latch plate-engaging faces of the assembled armature and magnet. Often times the permanent magnet, which is cast, has hidden voids which are exposed when grinding. This results in an unsightly pitted appearance on the face of the magnet. In addition, the exposed pits or pockets tend to collect dirt which may become lodged between the face of the magnet and the latch causing an air gap between the two which results in the loss of efficiency described above.
It also is generally desirable to plate the various parts of the magnet assembly particularly when the device is to be used in an atmosphere which may tend to corrode its parts. Typically the parts are plated before they are assembled. When the permanent magnet and armature are subsequently assembled, usually by press fitting them together, it is not uncommon for the plating to become scratched which exposes the underlying metal to the corrosive atmosphere. Because of the scratching which sometimes occurs during assembly, it is not uncommon to require that the entire device be plated again after assembly. This, of course, adds to the cost of the device. In addition, even when the assembled device is finally plated, the various etching solutions employed in the plating process may become lodged in cracks and crevices of the assembled pieces which is undesirable. In some instances, efforts are made to isolate the corrodable parts of the magnet assembly by potting it in a resinous material. This also adds to the cost of the magnet assembly.
It is among the general objects of the invention to provide a magnet assembly which avoids the foregoing difficulties.